Missile guidance system



Sept. 19, 1961 o. J. BALTZER MISSILE GUIDANCE SYSTEM 2 Sheets-Sheet 1 Filed Aug. 17. 195] NOSE /A NTENNA\ MISS/LE HE ADI/V6 GROUND 001V 7' ROL STA T/OIV INVENTOR. 0770 J. BALTZE/i 1 I I I SERVO CONTROL STEERING SYSTEM HYDRAULIC REGEI'VER AND TAIL ANTENNA ASSEMBLY FIG. 2

Sept. 19, 1961 o. J. BALTZER 3,001,186

MISSILE GUIDANCE SYSTEM Filed Aug.

2 Sheets-Sheet 2 FIG. 4.

INVENTOR 0770 J BALTZER ATTORNEY Filed Aug. 17, 1951, Ser. No. 242,255 8 Claims. (Cl. 343-6) The present invention relates to homing guidance of a missile in response to radar signals originating in the missile, and reflected from a target; more particularly it relates to a missile guidance system wherein the missile emits radar signals some of which strike a prospective target, echoes thus produced being picked up by a ground radar station, which thereupon transmits signals to the missile to guide it into the target.

It has been proposed heretofore to provide homing radar receiving apparatus in a guided missile but this would require sensitive and hence delicate circuits and devices in the missile, which would increase its complexity, bulk and weight, and moreover would tend to decrease its reliability. It is thought to be considerably better practice to locate only the transmitter portion of the homing radar system in the missile, as the transmitting devices are much simpler and far more rugged than the receiving apparatus.

An object of the invention, therefore, is to provide a missile homing system wherein the guided missile carries only the relatively simple elements of a microwave transmitting system, the more complex receiver and intelligence sensing circuits being maintained at an auxiliary ground station.

Another object is to provide a missile homing system wherein the missile is guided into the target by signals transmitted to said missile firom a ground station.

A further object is to provide the guided missile with a transmitter and means for producing scanning lobes of radiation to scan the perspective target.

An additional object is to provide a guided missile having a separate antenna system at each end for energy transmission purposes, said systems being connected to one another within the missile by tnansposing means.

Another object is to provide means for controlling the relative amounts of energy radiated by these two antenna systems.

A further object is to provide means for preventing radiation from the antenna system in the forward or nose end of the missile before the missile approaches within homing range of the target.

Another object is to provide continuously acting microwave phase shifting means to perform the target scanning function.

Other objects and many of the attendant advantages of this invention will be appreciated readily as the same becomes understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein: Y

FIG. 1 is a diagram illustrating the geometrical relationships involved in a guided missile homing system embodying the invention;

FIG. 2 is a diagram of the radar transmitter and microwave phase shifter carried by the missile, and showing also the transposed antenna systems connected thereto;

FIG. 3 is a diagram showing the scanning patterns of radiation at the two ends of the missile; and

FIG. 4 is a schematic view showing the paths of transmitted and reflected wave energy passing between a missile in flight, a target, and the ground control station employed, during guidance of a missile in accordance with the system of the present invention.

Referring first to FIG. 1, a guided missile 1 is shown 2 in flight with its longitudinal axis indicated by the line AA. A ground radar station G is located as shown, on the terrain below, and serves to control the'trajectory of the missile. p I

It will be noted that ordinarily the missile axis is not directed toward the target T, nor does it pass through ,6. This is due in part to the fact that normally the target is not at rest, but usually is moving'at high speed, in an arbitrary direction. With the missile direction as shown, the target would be moving to the left, say T, so that eventually missile and target will meet.

The elevation angle made by the line of sight to the missile from G is 0. It should be noted that this angle, in general, is different from the angle between the missile axis and a horizontal plane. In FIG. 1 the lines GG and HH' are both horizontal and also are parallel. The angle between line GH and line HA is designated ,6, the angle A'HT is called 5 and the angle THH' is 'y, the bearing of the target with respect to the missile.

Let it be assumed that it is desired to fly the missile along a trajectory that maintains angle 7 at a constant value, which will eventually cause the missile to collide with the target, as is well known. This requires, from the geometry of FIG. 1,-that 'y=(B'-fi)+0, arrived at as follows:

Produce the line GH beyond H to G. Then the angle GHH' is equal to the angle 0 between lines HG and GG because HH' is parallel to GG. Angle A'HG" is equal to angle AHG, as they are vertical angles, hence angle A'HG" equals 5. But by inspection I It is convenient to treat the angle (6-5) as a unit hereinafter.

Upon diflerentiating both sides of Equation 1 with respect to time, the dilferential equation below is found:

It has been established that knowledge of the derivative d'y/a't constituting the first member of Equation 2 is necessary and sufiicient to provide a proportional navigational type of homing trajectory for the missile.

Referring now to FIG. 2, there is shown a diagram of a dual antenna system to be carried by the missile. It will be noted that two antenna horns are provided at each end of the missile, and that these horns are connected in transposed relationship by wave guides. In detail, paired and spaced-apart horns 10 and 11 are located at the nose of the missile, while paired horns 12 and 13 which are spaced apart in the same configuration as those of the first pair are located at the tail of said missile and are connected to horns 1t and 11, respectively, by wave guides 14 and 15, which extend substantially through the length of the missile. It will also be noted from FIG. 2 that energy is delivered to the two antenna systems from a single radar transmitter 16 through the common connection 17, and the two wave guide sections 18 and 19. A microwave phase shifter 20, the detailsof construction of which form no part of the present invention, is connected in section 19 and is provided with means for rotating it continually while the missile is in operation. 7 As a result, the missile emits rotating scanning electromagnetic radiation at both ends in the lobed interference patterns shown in FIG. 3. In this figure there are shown the pattern 21 of the lobes of radar energy emitted by the nose antenna system 10, 11 of missile 1, and the patter-h 22 of the energy emitted by the tail antenna system 12, 13. Usually the transmitting system is so designed and/ or adjusted that most of the radiation, say percent of the total, is emitted by the nose system, the remainder be ing radiated by the tail system. This energy division may be accomplished by means of a microwave power divider '23, the details of construction of which form no part of present invention.

Due to the transposition of the wave guides i4, 15, E16. 2, these two patterns are continuously swept or scanned in the same sense, as indicated by the curved arrowsinFiG. 3.

4 In operation, after the missile has been launched against a prospective target, which has been located and is being tracked by the ground radar station at G, guidance impulses are sent to the missile 1 from said radar station to cause the missile to follow a course that will eventually cause it to collide with the target.

-At first, all the guidance is provided solely by the ground radar transmitter, on the basis of the information it secures from its own tracking of the target. 'However, such guidance can be only approximate at best, because the ground radar beam unavoidably spreads with distance, so that the error will increase with and be substantially proportional to the missile progress along its trajectory.

As the missile approaches the target, sufficient radiation from the transmitter 16 within the missile eventually will strike the target T and produce an echo that will be received by the ground radar G. This will alford accurate information of the relative location of missile and target and in response thereto the ground radar G will issue corrected signals or impulses to the missile to guide .it into the target.

It will be understood that while without the echoes of. the missile-originated radar pulses from the target, the accuracy of guidance attainable by the pulses beamed .from the ground radar and based on conventional tracking would diminish with increasing missile distance from the ground radar, the contrary is true when said echoes form the basis of guidance, for these increase in precision asthe distance between missile and target decreases.

flhe signals radiated from the tail antenna system 12, 13, of the missile may be received directly by the ground radar station at G. Obviously these direct signals are .unusually strong compared with radar pulses reflected from a target, hence only a relatively small portion of the output of the missile-borne transmitter need be radiated from the tail antenna system, leaving the major portion of the power to be emitted from the nose antenna system 10,11 to scan the target.

The radiation from the tail antenna system may be used to measure the angle p at the ground radar station G. it .is not requisite, however, that separate measurements bo-made ofboth B and it is in fact sufficient to deter- .mine the rate of change of their difi'erence (,B';3). This quantity has already been discussed above. The actual measurement may consist merely in employing the relatively strong tailsignal, having an envelope phase that is determined by 49', as a reference channel .signalin a suitablephase comparator circuit, with the target echo whose envelope phase is determined by d, as the other signal in thecomparator circuit. Such a comparator system would permit determiningthe difference vector (de/dtale/dt) For the complete solution of differential Equation 2, it is further necessary only to determine dH/dt. Here an approximation may be made, for it is found that the angle 0 changes at such a low rate that for typical targets at ground ranges exceeding 10 miles its .time rate will be considerably less than -l per second. This small value may .either be neglected entirely, or perhaps better, may be estimated with suflicient precision at the ground station.

After d'y/dt has thus been determined from measure ment or estimation of the parameters in the second member of Equation 2, it is then necessary merely to communicate the necessary steering information to the missile .from the ground station at G. Means for accomplishing lthis, the so-called command guidance methods, are 'already well known.

Essentially such command-guidance missiles or, alternatively, beam riding missiles include radio receivers that are responsive to properly coded pulses from a groundbased radio or radar transmitter. These receivers in turn, through suitable amplificrs, "control the valves of a hydraulic servo system which is suitably mechanically connected to the aerodynamic steering devices of the missile, such as the vanes that control the motions of the said :missile in various senses.

it will he understood, therefore, that the missiles :used in carrying out the present invention will carry such equipment or equivalent devices, whereby the missile may be steered by remote control by means of a suitable communication link with a ground-based radio or radar station. :Such equipment, however, designated as a whole by reference character 25, FIG. 2, .forms no part of the present invention. For details thereof reference should be made to the US. patent application, Serial No. 162,902, filed May 19, 1950, by William C. Parkinson etal., and entitled Method and Apparatus for Remotely Controlling an Airborne Vehicle.

Many interesting possibilities are available with this 'invention. An extremely'important feature is that the missile-home electronic equipment may be materially reduced in quantity and compleX ty, since the responsibility of deriving the requisitehomingintelligence rests with the ground radar apparatus, whose delicacy, complexity,'bulk and weight are of re'latively'little importance, as they are not .air horne nor subjected to shock and vibration as are those carried by a missile.

For example, a high-performance homing super'heterodyne receiver, such as would form part of the ground equipment, is obviously considerably more delicate and vulnerable than a magnetron transmitter, which wou'ldbe carried by the missile. No local oscillator or sensitive intermediate frequency amplifier need be carried by the missile and there are no associated automatic frequency control difiiculties within the missile. Furthermore, the complicated problem of range gating and automatic gain control of the proper target signal resides at the ground station, and .not 'in'the confined missile space.

Automatic means, preferably triggered by properly coded pulses from'the ground radar or by a suitable time delay.mechanism,'may'be provided in the missile to prevent emission of.radiation from the nose antenna system before the missile has approached within the desired homing range of the target. A mechanical shutter or other wave .guide switch mechanism 24, may be employed in the nose antenna assemblyfor this purpose. While this is not essential to the operation of the system, it maybe desirable as a means of preventing the enemy from detecting the missile prematurely.

Obviously the radar ranging or detection problem is not changed in any Way by carrying only the homing transmitter in the missile instead of mounting only the homing receiver-in thernissile, with the transmitter 'on-the ground.

The elimination of the need for a missileecarried gyroscope, otherwise required 'for measuring the rotation of the missile is-another-important simplification secured by the present invention.

It should be noted that .the composite system here set up is sensitive essentially-to motion of the target lineof sight alone, instead of angular movements of the missile itself. This applies to "allthe motions, namely yaw, pitch and roll. The reason this is true is'that any of these motions'will introduce identicalphase shifts in both the B and the ,8 signals, which thus cancel out in the diflerence expression (p'fl) 'as well as inits time derivative.

A considerable "improvement in the dynamic control and stability of the missile may be obtained-throughuse of the present invention. By continuous measurement of 3' and the attitude 'o'fthe missile, at the ground station, it becomes possible to tai1or'the command signal being sent to the missile 'in such way as to improve the stability characteristics thereof. It may, in 'fact, even be found preferable to make use of the signals from the tail end of the missile at all times, even during the midcourse guidance trajectory phase, in order to bring the missile into better position and control even before the homing period, to increase the accuracy of the final run into the target by homing.

Another advantage of the invention is that the instant at which radar beam guidance of the missile into the general vicinity of the target ends and homing guidance begins is no longer required to be determined by the missile itself, but is controlled by the much more elficient and elaborate ground station, which can act with greater precision. Furthermore, a ground-based receiver is usual- 1y better capable of detecting a target in the presence of chaff or other countermeasure devices, especially in view of the fact that ground stations can be attended by human operatives while all such functions when carried out by the missile must of necessity be automatic and consequently lack discretion.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A system for guiding a missile to intercept a target, comprising a source of electromagnetic wave energy carried by the missile, a control station remote from the missile, means on said missile for projecting part of the energy from the missile into the region containing the target, means for projecting a portion of the energy from the missile toward said control station, and means at the control station combining the energy reflected from the target and the energy projected toward said control station from the missile for controlling the missile.

2. A system for guiding a missile to intercept a target, comprising a source of electromagnetic wave energy carried by the missile, a control station remote from the missile, means on said missile for projecting part of the energy from the missile into the region containing the target, means for projecting a portion of the energy from the missile toward said control station, means at the control station for receiving the energy reflected from the target and the energy projected toward said control station from the missile, said last-named means being so constructed and arranged that steering information can be computed at said control station for maintaining a constant bearing angle between said target and said missile, and means at the control station for transmitting said computed information to the missile.

3. A system for guiding a missile to intercept a target, comprising means carried by the missile for generating high frequency electromagnetic wave energy, means adjacent the nose of the missile for radiating part of said energy in a forward direction from said missile, means adjacent the tail of said missile for radiating part of said energy in an aft direction from said missile, means for causing the forwardly directed energy and the aft directed energy to scan the regions ahead and behind the missile, and a control station remote from the missile combining the target reflected wave energy and the aft directed wave energy for controlling the missile, said control station being so constructed and arranged that steering information can be computed at said control station and transmitted to the missile for maintaining a constant bearing angle between said target and said misile.

4. A system for guiding a missile to intercept a target, comprising a source oi electromagnetic wave energy carried by said missile, a control station remote from the missile, means on said missile for projecting part of the energy from the missile into the region containing the target, means for projecting a portion of the energy from the missile toward said control station, means for causing said energy to scan the regions forward of and aft of the missile, means at the control station for receiving and comparing the energy reflected from thetarg'etand the energy projected toward said control station from the missile, said last-named means being so constructed and arranged that steering information can be computedat said control station for maintaining a constant bearing angle between said target and said missile, and means at the control station for transmitting said computed information to the missile.

5. A system for guiding a missile to intercept a target, comprising a source of electromagnetic wave energy carried by said missile, a control station remote from the missile, means on said missile for projecting part of the energy forward of the missile into the region containing the target and the remainder of said energy toward said control station, means for causing said projected energy to scan, means at the control station for comparing the energy reflected from the target and the energy projected toward said control station from the missile, said lastnamed means being so constructed and arranged that steering information can be computed at said control station for maintaining a constant bearing angle between said target and said missile, and means at the control station for transmitting said computed information to the missile.

6. A system for guiding a missile to intercept a target, comprising a source of radio frequency energy carried by said missile, a control station remote from the missile, an antenna system adjacent the nose of said missile for projecting part of the energy from the missile in an interference radiation pattern into the region containing the target, an antenna system adjacent the tail of said missile for projecting a portion of the energy in an interference radiation pattern from the missile toward said control a station, means connected to said antenna systems for causing scanning by the radiated energy, and means at the control station combining the energy reflected from the target and the energy projected toward said control station from the missile, said last-named means being so constructed and arranged that steering information can be computed at the control station and transmitted to the missile for maintaining a constant bearing angle between said target and said missile.

7. A system for guiding a missile to intercept a target, comprising means carried by the missile for generating high frequency electromagnetic wave energy, spaced radiators adjacent the nose of the missile for radiating part of said energy in a forward direction from said missile, similarly spaced radiators positioned adjacent the tail of said missile for radiating part of said energy in an aft direction from said missile, said radiators providing an interference radiation pattern at each end of the missile, means for causing the forwardly directed and the aft directed interference radiation patterns of electromagnetic energy to continually scan the regions ahead and behind the missile, a control station remote from the missile combining the target reflected wave energy and the aft directed wave energy, said last-named means being so constructed and arranged that steering information can be computed at said control station for maintaining a constant bearing angle between said target and said missile, and means at said control station for transmitting said computed information to the missile.

8. A system for guiding a missile to intercept a target, comprising a radio frequency transmitter carried by the missile, said transmitter providing a source of high frequency electromagnetic energy, a ground control station remote from the missile, a pair of spaced antennas mounted at the nose of said missile, a similar pair of spaced antennas mounted at the rear of said missile, microwave conductors interconnecting the antennas of the pair adjacent the nose and the transmitter, other microwave conductors interconnecting the antennas adjacent the nose of the missile and the antennas adjacent the tail of the missile in transposed fashion, said antennas providing an interference radiation pattern of energy projected forward and aft of said missile, means inserted in the conductors 7 ini rcpmmiag sa aged ramaanas adjac nt the 11955: oi the missile i0: @hangmg 1th? phase of 1h; anc gy mitted by townelot said v-antegnas with respect to the phase @I like energy smitted by the other of said antennas, thereby causing the projected energy to scan the regiens forward and of he missile, said ground control station -including means for receiving and comparing the signals plgjcgts iOIWaLdly and rearwardly of said missile whereby st ering ini rrnatioa can be s mpu l d at the nnlrrol 19 station ior maintaining a cons ant aring angle between a 'l t and said missile, and means at the cen ral statigm .ior transmi lmg me kcgm pntcd inimzma ion to -thc missilelieieremas Qi d in 111a zfille :Qf :this patent STATES PATENTS Dinga v Am. 2,. 1945 Eatqn l June 17,.1947 Ros; et al V 111.1) 15., .1947

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